The present invention relates to the field of dental prostheses and more particularly to dental appliances incorporating a joint for avoiding application of stress to abutment teeth during mastication.
When a patient loses only some of his teeth, it is common practice to provide a removable appliance which will support false teeth for co-operation with the remaining teeth so that the patient can chew normally. Such appliances are retained in the correct position in the mouth by retainers which encircle the abutment teeth. There are several types of retainers: clasps, which encircle the tooth; semi-precision attachments, which partially encircle the tooth; and precision attachments, which are all internal and do not encircle the tooth. If these appliances are rigidly constructed, stresses induced by chewing are transmitted to the abutment teeth. The Stress Breaker Appliance.RTM., U.S. Pat. No. 3,999,297, solved the problem of transmitting stress to the abutment teeth by separating the appliance into at least two segments and then joining the segments with a special wedge shaped joint which allows small, guided motion of the portions relative to each other. The features of U.S. Pat. No. 3,999,297 are easily incorporated into a dental appliance by means of the investment casting or lost wax process. In fact molding kits for this purpose have been available for many years.
While the invention of U.S. Pat. No. 3,999,297 provided a great advance in the field of dental prostheses and provision of the molding kits made the dental technician's life easier, it was found by the inventor that a number of features of the original Stress Breaker Appliance.RTM. could be improved. First, the female portion of the joint is joined to the frame of the rear portion of the appliance. Thus when repairs are needed, it is necessary to remanufacture the rear frame or at least perform major reconstruction. Second, since the female portion is so small and its faces so occluded, less skilled technicians have difficulty in making defect free castings. Third, once defects are introduced, they are difficult to remove.
If an improved female portion were to be developed which could be manufactured by less painstaking and less costly methods, and which could be incorporated into the dental plastic rather than into the frame, this would represent a great improvement in the Stress Breaker Appliance.RTM. and satisfy a long felt need of dental technician. Also, an improved female portion would enable less expensive manufacture of dental appliances.